The present invention relates to vehicle suspension systems, and more particularly to suspension systems that include an auxiliary spring on which a vehicle rides when lightly loaded.
Vehicles that are intended to carry heavy loads have suspension systems with appropriately high spring rates. When the vehicle is empty or only lightly loaded, the relatively small forces acting on the springs are not sufficient to produce significant deflections and the vehicle has an extremely rigid ride. The lack of effective spring action is not only jarring and uncomfortable, but is dangerous because an unsprung axle has poor traction.
While the above problems of heavy duty suspension systems are most commonly associated with trucks and semi-trailers, they are shared by other types of vehicles as well. Off-the-road vehicles, such as dune buggies, for example, are usually provided with very rigid springs in relation to their weight to withstand the rough treatment for which they are intended. When driven on smooth paved highways, their suspension systems are largely ineffective.
To overcome the above problems, some heavy duty suspension systems have been provided with auxiliary springs having a relatively low spring rate that are positioned between the frame of the vehicle and the main leaf springs. When the vehicle is lightly loaded, it is given a resilient ride by the auxiliary springs while the mainsprings remain relatively rigid. When heavily loaded, however, the auxiliary springs assume a fully flexed position and the vehicle rides on the mainsprings.
A suspension system, known as the "Empty Ride System" that includes generally U-shaped auxiliary springs for lightly loaded conditions is described in U.S. Pat. No. 3,194,580, issued to B. C. Hamlet on July 13, 1965. That system, however, requires specially designed hangers for the main leaf springs and, therefore, is not well suited for attachment to the many existing vehicles that are not equippped with auxiliary springs. Moreover, Hamlet's system, while used on many trucks, has not been adapted for use on off-the-road vehicles. Another problem associated with the Hamlet suspension system is that the configuration of the auxiliary springs includes a reverse bend, and the stresses on those springs are concentrated at the bend, thereby limiting their useful life.
The primary objective of the present invention is to provide a suspension system having improved and longer lasting auxiliary springs that can be readily added to a variety of existing vehicles despite variations in the configuration of the frames and springs of theose vehicles. Another objective is to provide a suspension system having auxiliary springs that is compact and requires a minimum space under the vehicle frame so as not to interfere with the action of the mainspring when the vehicle is heavily loaded or subjected to high shock loads.